Plant growth depends at least in part on interactions between the plant and microorganisms that habitate the surrounding soil. For example, the symbiosis between the gram-negative soil bacteria, Rhizobiaceae and Bradyrhizobiaceae, and legumes such as soybean, is well documented. The biochemical basis for these relationships includes an exchange of molecular signaling, wherein the plant-to-bacteria signal compounds include flavones, isoflavones and flavanones, and the bacteria-to-plant signal compounds, which include the end products of the expression of the bradyrhizobial and rhizobial nod genes, known as lipo-chitooligosaccharides (LCOs). The symbiosis between these bacteria and the legumes enables the legume to fix atmospheric nitrogen for plant growth, thus obviating a need for nitrogen fertilizers. Since nitrogen fertilizers can significantly increase the cost of crops and are associated with a number of polluting effects, the agricultural industry continues its efforts to exploit this biological relationship and develop new agents and methods for improving plant yield without increasing the use of nitrogen-based fertilizers.
Another known and well studied symbiotic association between plants and soil microorganisms involves arbuscular mycorrhizal (AM) fungi. This group of fungi, recently renamed Glomeromycota, is widely distributed throughout the plant kingdom including angiosperms, gymnosperms, pteridophytes and some bryophytes (Smith and Read, 2008). Among the angiosperms, at least 80% of the species can form AM symbioses, the only major exceptions being Brassicaceae and Chenopodiaceae. Arbuscular mycorrhizal fungi are able to transfer rare or poorly soluble mineral nutrients such as phosphorus, zinc and copper from the soil to the plant, which in turn provides carbohydrates to the fungus. This exchange of nutrients can be of critical importance when soil fertility and water availability are low, conditions that severely limit agricultural production in most parts of the world (Smith, et al., Mycorrhizal symbiosis. 787 pp., Academic Press. (2008)).
In addition to symbiotic relationships with microorganisms, healthy growth requires plants to extract a variety of elements such as phosphorus and micronutrients (copper, iron, zinc, etc) from the soil. Soils can oftentimes be deficient in these elements or contain forms of the elements that cannot be readily assimilated by the plant. Fertilizers are typically applied to soils to increase the amount of phosphorus for plant uptake. However, the vast majority of the phosphorus applied is rapidly converted to forms that cannot be utilized by the plant. Various fungal strains of Penicillium (e.g., P. bilaiae) and Rhizobium spp. have been applied to soil to facilitate uptake of phosphorus by the plant. See, e.g., U.S. Pat. Nos. 5,026,417 and 5,484,464 and U.S. Patent Application Publication 2010/0099560.
Continuing efforts are made to exploit these types of relationships between plants and microorganisms with the goal of increasing plant growth and yield. One such effort is in the field of inoculants with specific efforts being devoted to enhancing “on-seed” inoculant technologies and in particular, to enhancing the survivability of inoculants once they are applied to a seed. One such cause accounting for low survivability of inoculants include, among other things, the presence of incompatible compounds existing in seed treatments. Such compounds may include preservatives or other biocides used in seed treatment ingredients.
U.S. Pat. No. 4,149,869 discloses seeds coated with a mixture containing a caseinate salt and viable rhizobia bacteria.
EP. Pat. App. Pub. No. 0454291 discloses a process for producing an enhanced Rhizobium inoculant.
U.S. Pat. No. 5,106,648 discloses a method for coating seeds, however, the disclosure states that it is necessary to use Rhizobial strains that are resistant to fungicides to allow seeds to be coated with fungicides at the same time.
U.S. Pat. App. Pub. No. 2008/0132411 discloses a method for improving the survival and viability of microorganism inoculants on the seeds comprising the step of coating seeds with a mixture comprising a carbohydrate, a sugar alcohol, and microorganisms.
U.S. Pat. App. Pub. No. 2012/0208699 discloses methods and compositions for reducing the bridging of treated seeds, including some that also enhance the survivability of any beneficial microorganisms included in the composition or mixes therewith and/or enhance the yield of the plants that grow from the seed to which the treatment is applied.
Pat. App. Pub. No. WO 1994/06732 discloses a method obtaining a wettable powder inoculant formulation for use with leguminous crops.
Pat. App. Pub. No. WO 2006/071369 discloses a method for producing a liquid inoculant containing a desiccant, wherein the method can improve the survival and stability of bacteria in liquid inoculants in pack and on seeds.
Dey, B. P., Engley Jr., F. B., (1994). Neutralization of antimicrobial chemicals by recovery media. J. Microbiol. Methods. 19: 51-58 (discloses the ability to neutralize a variety of antimicrobial agents using a neutralizing medium to recover Staphylococcus aureus strain ATCC 6532 from tile surfaces exposed to a commercial pphenol and a quaternary ammonium compound).
A need remains, however, for compositions and methods that can enhance the survivability of microorganisms when compounds that are not compatible with microbially based inoculants are used as part of a seed treatment.